Our purpose was twofold: to determine the distribution of the endogenous photosensitizer Protoporphyrin IX in the uterus and the interval leading to maximal endometrial fluorescence following intrauterine instillation of 5-aminolevulinic acid (ALA). Our results showed that ALA-induced fluorescence could be first detected in the superficial endometrial glands 75 minutes after drug injection. In the endometrial gland stumps fluorescence intensity peaked 4-8 hours after ALA instillation and was more than 48 times higher than in the underlying myometrium. Fluorescence in the endometrial glands suggests that selective photodynamic destruction of the endometrium may be possible 4-8 hours after intrauterine ALA instillation.